1. Field of the Invention
The present invention relates to a method for testing a vibration damper of a motor vehicle in the installed state, and to a vibration damper test system for a motor vehicle.
2. Description of Related Art
Conventional vibration dampers include a spring as well as a damping element and are used both to ensure the driving safety of a motor vehicle and to optimize the driving comfort. The driving safety is heavily influenced by the road grip of the tires. Vibrations of the tire masses are therefore often minimized by strong damping. On the other hand, satisfactory driving comfort requires rather weak damping. A comprise between hard safety damping and soft comfort damping must therefore be sought when configuring vibration dampers.
A vibration damper installed in the motor vehicle is subject to wear in the course of the driving operation and changes its vibration behavior and its damping characteristic, so that a safety-critical state is frequently reached after a period of time.
To check the performance of vibration dampers, they can be uninstalled and measured on a separate test stand. This test method does indeed supply precise test results but it is impractical for time and cost reasons because of the deinstallation work and therefore is used very infrequently.
From the published European patent document EP 0 611 960 B1 and published German patent document DE 43 05 048 A1, a method for testing a vibration damper of a motor vehicle is known, in which vibrations are introduced into the motor vehicle's wheel suspension, in which the vibration damper to be tested is situated, via a vehicle wheel standing on a wheel contact patch, the vibrations being brought about by base point excitation vibrations; the damping behavior is determined in the process in that the differences from the motional amplitudes and the motional speeds of the wheel and of the vehicle body are related to the acceleration of the wheel or the dynamic vertical force, and the damping coefficient is estimated from this relation in that, for testing the quality of the vibration damper, the estimated damping coefficient is compared to a reference value and for the quality test it is determined whether a deviation from the reference value lies within a tolerance range.
This requires complex test stand actuator systems, which induce vibrations of the motor vehicle. Furthermore, it has become apparent that the reproducibility of the measurements is not always ensured, and that the measured values for the vibration damper describe the damping characteristic only to an unsatisfactory degree.